Efforts to relieve world-wide shortages of protein have included various bio-synthesis processes in which single cell protein (SCP) is produced by the aerobic aqueous fermentation of one or another of a variety of fungi, yeasts, or bacteria on various carbon energy substrates.
Attention has centered on carbon energy substrates which are readily available, cheap, uniform, safe, and preferably relatively water-soluble, such as the lower saturated aliphatic alcohols, primarily of 1 to 4 carbon atoms, and most generally methanol and/or ethanol.
In conventional aerobic aqueous fermentation processes, a limiting cost factor has been the loss (wastage) of the carbon substrate to carbon dioxide. Varying amounts of substrate actually become incorporated into the cell structure, for example roughly somewhat less than about half of the methanol and about 50 to 75% of the ethanol. The remainder of the substrate is converted to carbon dioxide and wasted as an off-gas. Even though various methods have proposed recovery of the carbon dioxide by employment thereof such as in a water-gas reaction, or reaction with a reducing agent such as methane to form additional methanol, or reaction with ammonia to produce urea, such schemes have not been found commercially viable, at least as yet.
Another problem encountered in conventional aerobic aqueous fermentation processes using carbon energy substrates has been the persistently low sulfur amino acid content of the produced single cell protein. Such SCP frequently requires supplementation with synthetically produced sulfur containing amino acids.
I have discovered practical and effective solutions to these problems.